This specification relates to data processing and content presentation.
The Internet provides access to a wide variety of resources. For example, video and/or audio files, as well as web pages for particular subjects or particular news articles are accessible over the Internet. Access to these resources presents opportunities for content items (e.g., advertisements, audio files, or video files) to be provided with the resources. For example, a web page can include content item slots (e.g., advertisement slots) in which content items (e.g., advertisements) can be presented. These content item slots can be defined in the web page using a portion of code that causes a browser to request a content item for presentation in the web page when the browser renders the web page. A content item distribution system selects content items for presentation in response to the request. The content item distribution system can select the content items based on information included in the request and publisher specified preferences regarding the types of content items that are presented with the web page.